Voltage-limiting arc interrupter



R. R.PlTTMAN VOLTAGE-LIMITING ARC INTERRUPTER Fi1ed`Jan. 29, 1945 Jan. 6,` 1948.

I @Wwf Patented Jan. 6, 1948 UNITED STATES PATENT OFFICE VOLTAGELLIMITING Ano INTERRUPTER Ralph Rudman, Park Hill, Ark. Application January 29, 1945, Serial No. 575,081 1- claim. (c1. 17a-3o) This invention relates to excess-voltage protective devices for use with alternating current systems, for the purpose of preventing an excessive superimposed voltage rise n a conductor or connected apparatus, such as might be caused by lightning.

Among the objects of the Vinvention may be noted: (a) the provision in an arc extinguishing device embodying spaced conducting electrodes within an expulsion tube and a filler between the electrodes, of meansfor rigidly supporting the filler in lateral abutting relation `with the tube; (fb)r the provision of means for so distorting the electrostatic field prior to sparkover between the electrodes to cause sparkover to occur adjacent to the line of abutment of the filler with the tube; (c) the provision of a discharge path providing a low initial sparkover voltage along with an are pathk which may be taken by an arc following sparkover which varies in cross-sectional area, the length and area of the arc path being so related as to effect arc extlnguishment; and (d) the provision of a novel electrostatic flux control construction for reducing the sparkover voltage between the electrodes and along the abutment line to a quantity less than thatr of any other path between the electrodes.

With thel above andi other objects in view which will appear from the description, my invention resides in the novel arrangement for supporting the ller, and in the electrostatic field control arrangement for effecting sparkover along a predetermined desired path, together with the combination of elements for accomplishing arc extinguishment which are so disposed asy tor assist in effecting the desired flux control, thus making possible the attainment of the desiredv results with a minimum of parts, and greatly simplifying the structure.

In the drawing: Fig. 1 is an elevational View ofan embodiment of the invention, shown partly in section; Fig. 2 illustrates in elevation the external appearance of the' structure; and Figs. 3 and 4g are fragmentaryY sections taken respectively along the. lines. 3-3fand' 4--4 of Fig. l. Similar reference characters indicate like elements in the several gures of the drawing.

Referring detail to the embodiment of the invention illustrated, a tube Il, of insulating material, e. g. hard fiber, is internally threaded at its upper end, and threadedly engaged by the downwardly extending bushing of conducting material l5. Near and somewhat above the lower end of the tube Il a terminal bolt 22, of conducting material, having a diameter less than that of the bore of the tube extends transversely therethrough and outwardly externally of the tube. A bracket member 25', of some suitable metal (partially shown) is clamped between the nuts 24 and 25, the latter members threadedly engaging the outwardly extending portion of the terminal bolt 22, and thus providing a mounting and lower terminal for the device.

A cylindrical filler I8', of insulating material, e. g. hard ber, having a diameter less than that of the internal diameter of the tube Il, is beveled at its respective ends, andthe conducting upper and lower electrodes i9 and 20 respectively are tted onftlie filler in conformity with the bevel of the respective beveled ends, the upwardly andV downwardlyy extending arms of theV elec trodesbeing longitudinally spaced on the filler. The lower sloped or beveled surface of the elec-l trode 2i) rests on the transversely extending terminal bolt 22, and the adjustable metal terminal screw I2 extends downwardly through internal threads of the bushing l5 to engagement with the oppositely beveled upper surface of the upper electrode i9, rigidly wedging the filler it in lateral abutting relationship with the inner surface of the tube Il. The upper end of the adjustable terminal screw l2 is shown spaced from aconductor ill by the spark gap indicated bytheV numeral Il. i

To provide housing, asleeve 23 extends upwardly along the outer' surface of a lower-end portion of the tube l l, being held in place by the passage ofthe terminal bolt 22 therethrough. At

f its upper end, the sleeve 23' is provided with an outwardly extending flange for supporting the housing i6', the latter extending upwardly above the upper end 0f the tube I1. The upper end of the housing l@ is closed by the cover I4, which is clamped between the upper end of the bushing i5, and the lock nut I3' of the terminal screw l2. The housing I6 is preferably formed from weather-resistant insulating material, such as glass or porcelain.

A sleeve of conducting material 2l is tted tightly around the outside of the tube l1 between thetermin'al members of the'device. For reasons shortly to appear, the sleeve 2| is preferably beveled so that its greatest lengthwise dimension along the tube is nearest to the line of abutment of the filler i8 with the tube I1, and its smallest lengthwise dimension along the tube is along a line diametrically opposite the abutment line.

While such a construction is not essential to the successful operation of the invention, it is convenient for the purpose of describing the operation of the invention to assume that the longitudinal distance between the electrodes I9 and 20 along the line of abutment,` or from the portion 21 of the upper electrode I9 to the portion 29 of the lower electrode 20, is equal to the longitudinal distance along a line diametrically opposite the line of abutment, or from the portion 28 of the upper electrode I9 to the portion 30 of the lower electrode 28. It is essential that the conducting members are so coordinated with the insulating members that the weakest electrical path between the terminal members of the device is longitudinally along the ller between Athe electrodes I9 and 20. y

When an increasing voltage is applied between the electrodes I9 and 20, the electrostatic'ilux prior to gap sparkover from the electrode. I9 to the electrode 20 follows the path of lowest relucL tance, and is thereby concentrated along aline through the wall of the tubeY I1 betweenthe portion 21 of the upper electrode I9 and the uppermost portion 3| of the sleeve 2|, and along a line through the wall of the tube I1 between the lowermost portion 32 of the sleeve 2| and the portion 29 of the electrode 20. Relatively, only an insignificant amount of flux passes from the portion 28 of the leectrode I9 to the portion 33A of the sleeve 2| or from the portion 94 of the'sleeve 2| to the portion 30 of the electrode 20, because of the relatively wide separation of these conducting elements,

VAsa result of the above-mentionedvflux concentration, streamers are originated at the pointsof maximum flux density and 4extend respectively downwardly from the portion 21 of the electrode I9 and upwardly from the portion 29 ofthe lower electrode 20. These streamers in effect reduce the length and therefore the sparkover voltage of the gap to an amount less than that which would be required in their absence. For this reason, and despite the fact that the distance from the portion 21 to the portion 29 may be equal to the distance from the portion 28 to the portion 30, sparkover occurs along the abutment line rather than along any other path between the electrodes.

Any ensuing alternating current arc follows the sparkover path, thus setting up the desired condition for alternating current Vare extinguishment. Because once the alternating current arc is established along the path of greatest restriction, it immediately seeks the path of least restriction. In so doing, it moves peripherally around the filler, and is extinguished through contact with the relatively cold surfaces passed over and the attendant cooling gases evolved therefrom. In applying the device, it is necessary that the distance between the electrodes be sufficient that, under the conditions of operation, the normal circuit voltage will be incapable of sustaining an arc along the path of least restriction following its movement from that of greatest restriction. This is a consideration related to both length and relative diameters of iiller and tube, and as one example, a tube having a diameter of 3A, a ller having a diameter of i-", and an electrode spacing of 2", has been found to be a satisfactory combination for application to alternating current circuits up to voltages of 9 kv., R. M. S. A construction for causing the herein mentioned arc movement around the filler has been heretofore described in more detail in Patent No. 2,164,720, dated July 4, 1939, and issued to Ralph R. Pittman.

Preferably the sleeve 2| is formed of tempered steel or other material having high strength, so that it may also function as mechanical reinforcement for the wall of the tube. The maximum impact occurs along the abutment line, and it is along this line that the maximum length of sleeve is disposed.

The invention herein disclosed is similar in certainrespects to that shown in my copending application Serial No. 573,572, which, however, does not embody the means herein illustrated and described for controlling sparkover.

It is intended that the specic illustration and description ofthe invention herein' presented will be regarded as illustrative rather than limiting.

- Iclaim as myinven'tion:` f 1 A voltage-limiting are interruptor comprising a hollow 'tube'of insulating material having at least one end open, a cylindrical iiller'of insulating material extending longitudinally therein and partially filling said tube, means holding said ller in lateral abutting relation with'said tube, normally insulated conductingelectrodes spaced apart at the respective ends of said filler and arrangedto provide a preferentialsparkover path between them along said ller and within said tube, the sparkover path along the'line' ofabutment1 being substantially equal to that along the parallel'line diametrically spaced from said line of abutment, and'iiu'x control means for concentrating prior to sparkover the flux between said electrodes adjacent to the line of abutment of said filler with said tube', said flux control means comprising a sleeve of conducting material tted tightly around the outside 'of said tube in insulated relationship to at least one of said electrodes, said sleeve being provided with beveled ends and so mounted on said tube that the longest dimension of said sleeve is nearer to said line of abutment than to any other portion of said filler.

RALPH R. PITTMAN.

' REFERENCES CITED The following references' are of record in the file of this patent:

UNITED STATES PATENTS Number Y Name I Date 2,050,397 Torok Aug. 11, 1936 2,247,352 Ackermann July 1, 1941 2,108,465 Austin Feb. 15, 1938 2,164,720 Pittman July 4. 1939 2,169,110 Pittman Aug, 8, 1939 2,276,638 Ackermann Mar. 17, 1942 FOREIGN PATENTS Number Country Date 760,207 France Dec. 6, 1933 

